Features/JRuby 1.7

Summary

JRuby is an alternative Ruby implementation with fast growing user base due to its great performance in parallel tasks. Although JRuby 1.6.7 is already in Fedora, this feature brings in new minor version and better Fedora integration.

Current status

Detailed Description

Most of the packages that JRuby depends on are in Fedora just because of JRuby, so they can be safely updated.

Some dependencies are shared with other packages, so they will have to be discussed with their owners (see #Scope).

Integration with Fedora

Normally, each Ruby implementations ships with its own copy of RubyGems library. This is wrong because a) it's bundling, b) there is no reason why multiple Ruby implementations wouldn't be able to share one RubyGems library. There used to be some differencies in JRuby's copy of RubyGems, but the JRuby upstream has been very cooperative and managed to get them all merged into upstream RubyGems.

The integration will require changing Fedora's operating_system.rb (place for distro-specific defaults for RubyGems). This change will result into all Gems with binary extensions having to be recompiled, as the binary extension placement will change. See [1] for current operating_system.rb look and its changes from F18.

What should "/usr/bin/ruby" point to? During standard Gem packaging process, the executable files in Gems get shebangs according to the binary that they are packaged with (Ruby => "/usr/bin/ruby"; JRuby => "/usr/bin/jruby"). Therefore executing a Ruby "binary" runs the interpreter that was used for building (or the hardcoded one, which is usually Ruby). Using alternatives for "/usr/bin/ruby" doesn't seem to be a very good option, because Ruby and JRuby are not in fact full alternatives, as they for example cannot use same extension Gems (but it still makes sense to allow executing same binaries with them). Also, alternatives are only switchable on admin level (we want every developer with non-root privileges to be able to choose the interpreter). Therefore Ruby-SIG has come up with solution of having "/usr/bin/ruby" as a bash script (currently called rubypick) [2], that allows user to choose the interpreter as first argument on invocation (_mri_ or _jruby_), if such a parameter is present. Otherwise it falls back to a default. For example invoking "ruby_binary _jruby_ --foo=bar" in fact invokes "/usr/bin/jruby ruby_binary --foo=bar". This bash script will be in a separate package and both Ruby and JRuby will depend on it.

Ruby-SIG knows that this feature might be controversial and we wouldn't want it to stop us from bringing JRuby's power to Fedora (if met with a heavy resistance). So if anyone will suggest a more suitable solution, we'll go with it instead of this one.

Changes in packaging

None yet. JRuby will be able to use pure Ruby Gems packaged into RPM out of the box, but packaging of Gems with JRuby extensions is turning out to be very complicated, so the guidelines for it will be postponed to next release (as well as the actual packaging). Users will be still able to install Gems with JRuby extensions, both system-wide (into /usr/local/) and into their home directories.

Benefit to Fedora

JRuby is starting to get very popular among Rubyists, mainly because of its excelent performance in tasks using concurrency (leveraging power of JVM). Because of this, JRuby is mainly used for running web (mostly Ruby on Rails) applications under great stress. Having up-to-date and sanely packaged JRuby is a must for Ruby development and deployment platform.

Scope

The changes only affect Ruby packages in Fedora. Few updated Java packages (jansi, jcodings, jline2, snakeyaml; also some jnr-* dependencies of gradle) may also affect some dependent Java packages - this will have to be discussed with their owners.

New Packaging Guidelines

Some alterations were made to Ruby Packaging Guidelines. These will prevent breakage by the future introduction of JRuby-specific guidelines. The new draft can be seen at [1]. The draft has been proposed to FPC [2].

How To Test

1) There is a testing repo at http://bkabrda.fedorapeople.org/jruby/jruby.repo, which can be used to test. Do not install this on your system, due to the changes mentioned above, it would break your standard Ruby installation. This repo is meant to be tested in fedora-19-x86_64 mock chroot, where it can do no harm.

2) The repo also contains Ruby and basic set of Gems rebuilt with mentioned modifications (adoption to changes in Fedora-Ruby integration).

User Experience

JRuby will be up-to-date, usable and will be able to use Fedora's RPM-packaged pure Ruby Gems.

Dependencies

As mentioned, few Java packages, that are dependencies of some other packages, will have to be updated (see #Scope). Also, all the RubyGems packages with binary extensions will have to be rebuilt:

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